Classification of the secondary cardiomyopathies

SECONDARY cardiomyopathy is defined as heart muscle disease of known cause or association. Naming particular diseases is preferable where individual conditions are being referred to e.g. myocardial sarcoid, cardiac amyloidosis, scleroderma heart disease, since the term cardiomyopathy without qualification is generally accepted as referring to the primary forms. Nevertheless, a convenient collective term is needed to cover all the conditions which have to be excluded before a diagnosis of primary cardiomyopathy can be made. There are a very large number of such conditions and Hudson (1970) lists over 100. Faced with an exercise in classification of this magnitude most pathologists would first divide the conditions according to anatomical pathology, then consider the types of pathological reaction and finally the aetiology (Table 1). The material seen by the pathologist ranges from a single stained slide to the complete body for necropsy, with full clinical data. The first step is to exclude vascular or valvular conditions which may be responsible for the heart muscle disease. Of the vascular lesions, coronary atheroma is the commonest known cause of heart muscle disease, so much so, that ischaemic heart disease is not usually regarded as a secondary cardiomyopathy. Rarer causes of coronary occlusion such as vasculitis with thrombosis, or fibrosis following trauma (including cardiac surgery) should also be kept in mind. Valvular incompetence secondary to aortic wall disease may be due to cystic medionecrosis either as in the Marfan syndrome and similar uncommon genetically determined connective tissue disorders or more often as an isolated finding. It may also occur due to inflammatory changes as in ankylosing spondylitis and syphilis. Primary valve disease causing myocardial changes is mainly fibrotic as in rheumatic-type valve disease, or calcific as in isolated aortic stenosis. Less common underlying pathologies are perforation of valve cusps following infective